| Message |
Hey George. Damn! They broke your wheel! Well, I would first think that one possible reason they didn't heat your wheel is a fear of removing its clearcoat. I would have thought this would be a moved point in order to make the wheel the right shape again, but who knows what they were thinking. I would have suggested a 1-2 hour heat treatment at 260C (500F) to alleviate any stresses the curb put into the wheel. That's why they broke it in the first place: The microstructure of the wheel at the impact area was crazed with fracture sites, and the slightest bit of additional energy that is given to it (like they did to bring it back into shape) propagated the crack(s) through the wheel and it broke. There are limitations, however, on the temperature that you can bring an Al-Mg alloy up to. Aluminum melts at about 660C, and magnesium at 650C, but at temperatures as low as 450C, the alloy will melt (eutectic composition), so they would need to approach this temperature without getting too close (say 70% as a rule of thumb). Above 400C, you need to heat-treat Al-Mg alloys in an inert atmosphere or under vacuum - something most places can't do (we can!) Sulfur dioxide or carbon dioxide are cheaper than inert gasses (Argon, helium, etc.) but are harder to evacuate once you are done with them. The protective atmosphere would eliminate surface oxidation (which, if severe could decrease strength). This could have been tried AFTER the stress anneal. Anyway, I would have suggested only the stress anneal to restore the ductility to bend the wheel back into shape. Next time you hit a curb send the wheel to me, or buy yourself a big furnace and try it on your own! Like I said, let's just avoid those curbs! :) Good luck, hope you can find another wheel for cheap! Hope this helped. --SS
May those lost in the space shuttle tragedy find peace and harmony after their tragic death, 2/1/03. |
 |
03:02:48 02/04/03
